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LruCache.java
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LruCache.java
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import java.util.HashMap;
public class LruCache<K,V> {
private static class Entry<K,V> {
final K key;
V value;
Entry<K,V> prev;
Entry<K,V> next;
List<K,V> list;
Entry(K key) {
this.key = key;
}
void unlink() {
assert prev != null;
assert next != null;
assert prev != this;
assert next != this;
prev.next = next;
next.prev = prev;
prev = null;
next = null;
--list.size;
list = null;
}
};
private static class List<K,V> extends Entry<K,V> {
int size;
List() {
super(null);
prev = next = this;
}
void clear() {
while (next != this) {
next.unlink();
}
}
void append(Entry<K,V> e) {
assert e.next == null;
assert e.prev == null;
e.prev = prev;
e.next = this;
prev.next = e;
prev = e;
e.list = this;
++size;
}
Entry<K,V> first() {
assert next != this;
return next;
}
}
private final HashMap<K, Entry<K,V>> entries = new HashMap<>();
private final List<K,V> singleUse = new List<K,V>();
private final List<K,V> multiUse = new List<K,V>();
private final int maxSize;
public LruCache(int maxSize) {
this.maxSize = maxSize;
}
public int size() {
return entries.size();
}
public void clear() {
entries.clear();
singleUse.clear();
multiUse.clear();
}
public void put(K key, V value) {
Entry<K,V> e = entries.get(key);
if (e == null) {
if (entries.size() == maxSize) {
Entry<K,V> victim = singleUse.size >= maxSize / 4 ?
singleUse.first() : multiUse.first();
entries.remove(victim.key);
victim.unlink();
}
e = new Entry<K,V>(key);
entries.put(key, e);
singleUse.append(e);
} else {
e.unlink();
multiUse.append(e);
}
e.value = value;
}
public V get(K key) {
Entry<K,V> e = entries.get(key);
if (e != null) {
e.unlink();
multiUse.append(e);
return e.value;
}
return null;
}
public V remove(K key) {
Entry<K,V> e = entries.remove(key);
if (e != null) {
e.unlink();
return e.value;
}
return null;
}
public static void main(String[] args) {
LruCache<Integer, Integer> cache = new LruCache<>(2);
assert cache.size() == 0;
assert cache.get(1) == null;
cache.put(1, 1);
assert cache.size() == 1;
assert cache.get(1) == 1;
cache.put(2, 2);
assert cache.size() == 2;
assert cache.get(1) == 1;
cache.put(3, 3);
assert cache.get(2) == null;
assert cache.get(1) == 1;
assert cache.size() == 2;
assert cache.remove(1) == 1;
assert cache.get(1) == null;
assert cache.size() == 1;
assert cache.get(3) == 3;
cache.clear();
assert cache.size() == 0;
assert cache.get(3) == null;
}
}